The present invention relates to an apparatus and method for testing prosthetic heart valves under conditions simulating the circulatory system under which the valves are to be used. Accordingly, the present invention is particularly useful for mimicking the human circulatory system so that a heart valve may be placed therein, tested and observed for determining the suitability of the heart valve for actual implantation into the body. Thus, the present invention concerns the construction of a circulatory loop or defining a flow channel which loop includes various means for testing parametric values of the heart valve as well as including novel and non-obvious test chambers which actual mount the heart valve for advancement and orientation in the flow channel.
In recent years, the knowledge and skill of surgeons has dramatically increased in the cardiovascular field so that heart surgery has become somewhat commonplace. Statistically, one of the more common corrective surgical procedures in the pulmonary field replaces damaged or deteriorated auricle or ventricle valves in the human heart. As a result, the medical community demands an increased supply of prosthetic valves for surgical implantation. Accordingly, there is a corresponding need to ensure the reiliability of prosthetic valves before actual implantation, especially since the operation, while common, is nonetheless delicate and stressful on the patient. Accordingly, there is value in knowing the suitability and integrity of a prosthetic valve prior to the start of such surgery.
In the past, most techniques for testing heart valves have been directed to durability or fatigue testing of a single valve to see if the design of the valve suits its intended use. Such durability testing apparatus has been described in U.S. Pat. No. 4,381,663 issued 3 May 1983, and U.S. Pat. No. 4,546,642 issued 15 Oct. 1985, both of which were issued to Swanson. However, with increased demand for heart valves, manufacturers desire to test each heart valve for reliability and integrity rather than simple durability. The production line testing of prosthetic heart valves thus requires a machine capable of creating a proper physiological environment and then acquiring parametric data on the performance of the valve under test. In such a machine it must be possible to quickly and easily insert valves into the flow channel, test the valve and then remove the valve.
In the past, most circulatory simulating systems have included stationary heart valve supporting structures so that use of these devices require an initial draining of the system, the removal of the heart valve support, the positioning of the heart valve support in the mounting fixture and the reassembly of the flow channel with the heart valve in place after which the flow channel is charged with fluid. Understandably, with a complex flow channel, this procedure is extremely time consuming and is thus difficult to implement for production line testing. Indeed, prior art apparatus of the type just described often requires a period of up to thirty minutes to test a heart valve. Another danger resides in this technique, though, since biological heart valves must always be maintained in a moistened condition since the best available valves are constructed of organic tissue. Due to the time involved in draining and recharging the system, there exists the danger that the heart valve might become desiccated. If this occurs during draining the system, it is therefore possible that a valve that actually tested good subsequently becomes degenerate due to the drying out of the tissue during the draining of the system.
In order to eliminate the need for draining, disassembling, reconstructing and recharging the flow channel of prior art devices, one prior art test chamber has been developed as described in U.S. Pat. No. 4,450,710 issued 29 May 1984 to Nettekoven. In this device, a test chamber is provided for insertion into a flow channel with the mounting structure for the prosthetic heart valve comprising a shuttle into which one or two heart valves may be mounted. The shuttle means advances and retracts the heart valve into and out of the fluid flow while maintaining a dynamic seal between the shuttle carriage and the walls of the test chamber. While this patent differs from previous techniques, there still remains the possibility that a heart valve may become desiccated when it is not in position within the flow channel.
Another need resulting from the increased demand for prosthetic heart valves is the maintenance of production line testing of each valve for archival purposes. The value of having a permanent record of parametric test data as well as visual data for each approved valve is readily apparent when considering the increased propensity for malpractice and products liability claims. By production line testing of each prosthetic valve and the maintenance of an archival record thereof, manufacturers will later be able to demonstrate the integrity of a valve implanted in the human body, should such need arise. Further, an advantage of the present apparatus and method not heretofore available is the customizing of the testing procedure to correspond to a specific individual's circulatory system, should various parameter of the patient's pulmonary system be known, such that a specific valve can be tested, in vitro, in a manner that simulates the circulatory environment of the specific patient who will receive the valve. Thus, a valve may be tested under very close operating conditions on an individualized basis rather than under generalized test procedures.